This disclosure relates to steer-by-wire systems, and more particularly, to steer-by-wire systems with variable road feedback.
Conventional vehicular steering systems have an articulated mechanical linkage connecting the steering wheel to the steerable road wheels. Even with power assist, the operator of such a mechanically linked vehicle can generally feel the forces of the road against the steerable road wheels through the steering wheel. Indeed, this is a desirable feature of mechanical linkage steering that is sought out by operators and purchasers of high performance vehicles, as indicated by the popularity of so-called xe2x80x9crack-and-pinionxe2x80x9d steering.
With conventional mechanical linkage steering, the road forces felt in the steering wheel give the operator feedback useable to anticipate and control the vehicle. If this feedback is removed or substantially reduced, such as in the case of over-assisted or xe2x80x9cmushyxe2x80x9d power steering systems, the operator will have the uncomfortable feeling of being separated from the road wheels without sufficient sensory information to maintain precise control, and will therefore tend to oversteer the vehicle in demanding situations such as sharp or sudden turns.
A steer-by-wire steering system is defined as a steering system lacking a direct articulated mechanical linkage for connecting a steering wheel with a set of steerable road wheels. Such systems are desirable because they permit vehicle designers great latitude in the use of space that would normally be taken up by mechanical steering linkages. In effect, the steering wheel becomes a sophisticated type of joystick.
Accordingly, it is desirable to provide the operator of a vehicle equipped with steer-by-wire with feedback of road forces, or xe2x80x9croad feelxe2x80x9d, comparable to that of a vehicle equipped with conventional mechanical steering.
In an exemplary embodiment, a variable feedback device for a steer-by-wire system comprises a housing that contains a magnetorheological fluid, a magnetic field generator for generating a variable magnetic field within the housing in order to vary the viscous resistance of the magnetorheological fluid therein, and a rotor rotatably mounted within the housing that rotates through the magnetorheological fluid and is responsive to the variable viscous resistance thereof.
A steer-by-wire system comprising the variable feedback device has multiple sensors for generating input signals, including a steering column sensor for sensing changes in position or torque of a steering wheel and a wheel sensor for sensing changes in position or torque of a steerable vehicle wheel. The system also includes an electric power steering motor coupled to a steering system for assisting the vehicle operator, and a device housing. Contained within the device housing are a magnetorheological fluid, a magnetic field generator adapted to produce a magnetic field within the magnetorheological fluid, and a rotor rotatably mounted within the device housing, wherein the rotor is responsive to the resistance of the magnetorheological fluid.